Han Chuen Lim

Stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short PPLN waveguide

We demonstrate a stable source of high quality telecom-band polarization-entangled photon-pairs based on a single, pulse-pumped, short periodically-poled lithium niobate (PPLN) waveguide. Full quantum state tomographic measurement performed on the photon-pairs has revealed a very high state purity of 0.94, and an entanglement fidelity exceeding 0.96 at the low-rate-regime. At higher rates, entanglement quality degrades due to emission of multiple-pairs. Using a new model, we have confirmed that the observed degradation is largely due to double- and triple-pair emissions.

Broadband source of telecom-band polarization-entangled photon-pairs for wavelength-multiplexed entanglement distribution

Studies on telecom-band entangled photon-pair sources for entanglement distribution have so far focused on their narrowband operations. Fiber-based sources are seriously limited by spontaneous Raman scattering while sources based on quasi-phase-matched crystals or waveguides are usually narrowband because of long device lengths and/or operations far from degeneracy. An entanglement distributor would have to multiplex many such narrowband sources before entanglement distribution to fully utilize the available fiber transmission bandwidth. In this work, we demonstrate a broadband source of polarization-entangled photon-pairs suitable for wavelength-multiplexed entanglement distribution over optical fiber. We show that our source is potentially capable of simultaneously supporting up to forty-four independent wavelength channels.

Polarization-independent, wavelength-shift-free optical phase conjugator using a nonlinear fiber Sagnac interferometer

We propose and experiment with a novel configuration of a wavelength-shift-free optical phase conjugator using a nonlinear fiber Sagnac interferometer. In the proposed configuration, two orthogonally polarized pump waves are fed into different ports of the Sagnac interferometer, and we can achieve polarization-independent as well as wavelength-shift-free operation.

Distribution of polarization-entangled photonpairs produced via spontaneous parametric down-conversion within a local-area fiber network: theoretical model and experiment.

We present a theoretical model for the distribution of polarization-entangled photon-pairs produced via spontaneous parametric down-conversion within a local-area fiber network. This model allows an entanglement distributor who plays the role of a service provider to determine the photon-pair generation rate giving highest two-photon interference fringe visibility for any pair of users, when given user-specific parameters. Usefulness of this model is illustrated in an example and confirmed in an experiment, where polarization-entangled photon-pairs are distributed over 82 km and 132 km of dispersion-managed optical fiber. Experimentally observed visibilities and entanglement fidelities are in good agreement with theoretically predicted values.

Wavelength-multiplexed distribution of highly entangled photon-pairs over optical fiber

We report the first experimental demonstration of wavelength-multiplexed entanglement distribution over optical fiber. Forty-four channels of polarization-entangled photon-pairs were produced from a single pulse-pumped, short periodically-poled lithium niobate waveguide and distributed over 10 km of dispersion-shifted optical fiber. Entanglement fidelities of the distributed photon-pairs exceeded 0.86 for all selected channels.

Suppression of idler spectral broadening in highly efficient fiber four-wave mixing by binary-phase-shift-keying modulation of pump wave

Proposes and demonstrates a novel method of suppressing spectral broadening of the idler wave, which is generated in fiber four-wave mixing (FWM) pumped by a continuous wave. In this scheme, binary-phase-shift-keying (BPSK) modulation of the pump wave broadens the pump spectrum so that the Brillouin threshold for the pump power is increased, whereas it never affects the spectrum of the idler wave. By the 2-Gb/s BPSK modulation of the pump wave, we achieve a FWM efficiency as high as 10 dB, maintaining a side-band suppression ratio of the idler wave larger than 25 dB.

Polarization-independent optical demultiplexing by conventional nonlinear optical loop mirror in a polarization-diversity loop configuration

All-optical demultiplexing schemes based on cross-phase modulation in a conventional nonlinear optical fiber loop mirror (NOLM) switch generally suffer from a polarization dependence. In this letter, we propose a polarization-diversity loop configuration that allows polarization-independent all-optical demultiplexing by a conventional NOLM switch. We demonstrate polarization-independent all-optical demultiplexing of 40 Gbit/s signal pulses using the proposed scheme.

All-optical polarization-insensitive time-division demultiplexer using a nonlinear optical loop mirror with a pair of short polarization-maintaining fibers

We propose an all-optical polarization-insensitive time-division demultiplexer using a nonlinear optical-loop mirror (NOLM) with a pair of short polarization maintaining (PM) fibers. This configuration enables us to realize polarization-diversity operation of a conventional NOLM consisting of a non-PM fiber. When a signal pulse is launched on a PM fiber placed at the input port of the NOLM, the pulse is temporally separated into two pulses with orthogonal linear polarizations. Each polarization component is switched independently by the NOLM, and recombined by another piece of a PM fiber placed at the output port of the NOLM. We experimentally demonstrate that a 40-Gb/s signal is demultiplexed into 10-Gb/s channels independently of. signal polarizations.

Broad-band mid-span spectral inversion without wavelength shift of 1.7-ps optical pulses using a highly nonlinear fiber Sagnac interferometer

We demonstrate broad-band mid-span spectral inversion without wavelength shift of short optical pulses using a highly nonlinear fiber Sagnac interferometer. The 1.55-/spl mu/m optical pulses with a 1.7-ps pulsewidth are transmitted over 40 km of standard fiber, showing the suitability of this technique for broad-bandwidth second-order dispersion compensation in high-bit-rate optical fiber transmission systems.

A filter-free scheme for orthogonally pumped polarization-insensitive optical phase conjugation of broad-band optical signals

Orthogonally pumped four-wave mixing is known as an effective technique for polarization-insensitive optical phase conjugation in optical fibers. However, for phase conjugation of broad-band optical signals, a wide pump wavelength separation is a necessity in order to avoid crosstalks. This can result in an increase in polarization sensitivity of the scheme. As a solution to this problem, we propose a filter-free scheme that automatically rejects unwanted four-wave mixing products, such that broad-band optical phase conjugation can be achieved with a narrow pump wavelength separation for improved polarization insensitivity.